There are some sawbones here. Getting to urgent care or an emergency department is the right move at this point. I haven't read everything but I've read the trajectory of your comments. Your worry right now is that you're dealing with the early stages of cellulitis or the development of an abscess. If you haven't, begin tracking the margin of redness with a marker. And you absolutely have to tell the doctor it's from injection.
About the keflex, it's a lucky break because that's very likely what you would have gotten anyway. I don't know how many you have or what dosage, but the standard starting dose is 500 mg every 12 hours. This being meso, though, you might need to take 500 mg every 6-8 hours if you weigh more than 200-220 lbs. That is also the adjustment made if you experience systemic symtpoms -- fever, chills, malaise -- or if the infection spreads. If you have an immune condition or diabetes, opt for six hours if you have the meds for it. Again, track the margin.
VERY VERY IMPORTANTLY, you need to space your antibiotics out evenly until you get to the doctor. If you taking the more frequent dose means you'll have to go 12 hours without a 500 mg dose, do not increase frequency. Otherwise, you can kick off an even worse infection. This is the a real danger for you right now. If you have the 250 mg capsules, and you only have a few, this is especially crucial.
MRSA - keflex should abate the symptoms within 48-72 hours of initiation. If that doesn't happen, go to an emergency department because you need to treat against the possibility of MRSA. You may need IV antibiotics and you may need to be admitted. A history of MRSA, skin infections, or a spider bite appearance, or purulent discharge will warrant get you an rx for bactrim, doxycycline, or clindamycin. Make sure to mention you're an athlete, because if it's a toss up on whether or not to treat for MRSA absent a culture, athletes are at a higher risk.
Final point: if the keflex starts working, you still need to go to a clinic. You have to complete a full course of antibiotics. Taking some keflex and stopping before eliminating the infection to a level the immune system can handle is potentially more dangerous than not taking any at all. This is AT LEAST 5 days if you don't have a history of infections and the symptoms fade rapidly. If it's slow going, you need to take them for 7-10 days. At the moment, you're killing only the easiest to kill bacteria. If you stop the drugs too early, the gnarly ones are left.